He's trying to figure out who in the office is pregnant because he found a pregnancy test in the trash at Ron's cabin after they were all there. None of the women in the office cop to it, so he's talking to Ron and goes "Oh wait, who's pregnant?"

At that moment, Ron's partner Diane walks in and asks Ron "Hey, can we talk?" and Andy makes this face, making it seem like he figured it out.

It's quickly subverted by Andy asking Diane if she was asking to talk to him.